The rotary process for producing glass fibers is well known. Basically, it involves delivering a stream of molten glass to a spinning rotor or disc and allowing centrifugal force to cause the glass to extrude through small orifices in the disc sidewall. The resulting fibers are further attenuated and directed downwardly toward a moving collection belt or chain by a blast of air from nozzles or orifices in an air ring surrounding the fiberizing disc. The column of falling fibers is then sprayed with binder which is later cured when the coated fibers are moved through an oven.
If the movement of the column of fibers is unaltered it converges at a point in its downward path to a minor diameter. The primary reason for this phenomenon is that the cylinder of high velocity air leaving the air ring orifices creates a low pressure zone beneath the spinner disc, and the pressure zones do not find equilibrium until they reach a point between the bottom of the spinner disc and the collection chain. The location of the minor diameter is affected by a number of factors, including the velocity of the air from the air ring and the static air pressure surrounding the column. The resulting well-defined relatively small column diameter permits precise deposition of glass fibers onto the collecting surface. On the other hand, it tends to facilitate the amassing of individual fibers into ropey bundles, resulting in many voids throughout the product due to poor fiber density distribution. Also, such a column has a high velocity which aggravates blowback around the collection chamber walls which in multi-spinner chambers can further deteriorate fiber density distribution. A product produced from such a blanket has less than optimal thermal insulating and tensile strength properties.
To provide for more uniform deposition of the fibers it has been suggested to control the path of the fiber column by a variety of different means. Obstacles have been positioned in the path of the column to redirect its flow, pulsating air streams have been used to control the column and the fiberizing equipment itself has been oscillated to distribute the fiber column across the collection chain. Although a number of these modifications have produced beneficial results in the area of fiber collection, they have not satisfactorily improved product quality to the desired level.
A significant remaining problem is the difficulty in uniformly coating the fibers with binder so as to produce a product with less variance in physical properties from one portion of the product to another. When spraying binder from a number of inwardly directed nozzles mounted circumferentially around the fiber column, it is difficult to avoid uneven binder application due to the tendency of the small orifices to occasionally clog. Moreover, it is difficult for such a spray to uniformly penetrate the dense fiber column, leaving some quantity of fiber devoid of binder. Further, the overlapping spray pattern of such an arrangement often results in binder adhering to the chamber walls. In addition, the nozzles and support headers sometimes trap fibers which accumulate into wads before eventually being dislodged and deposited in the fiber blanket.
It has been suggested to introduce binder from within the fiber column while at the same time distorting the shape of the column by pressurized air, also delivered from within the column. The density distribution of the fibers can be improved by changing the shape of the column in this manner, and this method of applying binder results in better binder distribution and permits the use of a larger nozzle orifice, which reduces the tendency to plug. An example of such an arrangement is disclosed in U.S. Pat. No. 4,832,723, wherein the air and binder are shown as being applied through centrally mounted tubes extending below the rotary disc. Although this method is an improvement over previous methods of applying binder and controlling the shape of the fiber column, certain aspects of the method still leave room for improvement. The build-up of fibers and binder on the nozzle end cannot always be entirely eliminated, and the effect of the air blast on the shape of the fiber column can be less than desired when utilized in connection with large size discs.
It would be desirable to provide a method and means for better controlling the shape of the fiber column during production of fiber glass by the rotary process. It would also be desirable to improve the binder application method in conjunction with controlling the shape of the fiber column so that binder can be more uniformly applied to the fibers. Preferably, the binder application method would be suited for use with large diameter discs and would be capable of applying binder from within the column without permitting significant fiber and binder to build up on the binder spray nozzle.